A power train for hybrid vehicles typically includes a generator motor and a driving motor, each concentric with an input shaft, which receives power from an engine. A planetary gear set is disposed between the engine and the generator motor on one side, and the driving motor on the other side. Power is received from a ring gear of the planetary gear set and transmitted to a differential through a chain.
The generator motor is connected to a sun gear of the planetary gear set. The driving motor is connected to the ring gear. Carriers are connected to the engine.
The generator motor mainly starts the engine and generates electricity and the driving motor supports starting of the vehicle and power of engine.
When the vehicle starts, it is preferable to use a motor with excellent torque efficiency. Because the driving motor is connected to the ring gear, the capacity of the driving motor should be large to output sufficient driving force for the vehicle.
However, the large capacity of the driving motor in the configuration set forth above makes the power train too long and difficult to mount in a vehicle.